The present invention relates to printing onto textured, contoured or other three-dimensional substrates. The invention is particularly related to the printing onto such substrates as those having textile fabric surfaces or molded objects, rigid panels such as office partitions, automobile interior panels and other contoured objects, and to such printing using ink jet printing techniques.
Applying ink to a substrate by ink jet printing requires a proper spacing between the ink jet nozzles and the surface of the substrate to which the printing is applied. Normally, this spacing must be set to within one or two millimeters to maintain effective printing by an ink jet process. If the distance from the nozzles to the surface being printed is too great, deviations from ideal parallel paths of the drops from different nozzles become magnified. Further, the longer the flight path of the drops from the print head to the substrate, the more dependent the accuracy of the printing becomes on the relative speed between the print head and the substrate. This dependency limits the rate of change in print head to substrate velocity, including changes in direction. Also, the velocity of the drops moving from the print head nozzles to the substrate declines with the distance traveled from the nozzles, and the paths of such drops become more greatly affected by air currents and other factors with increased nozzle to substrate distance. Additionally, droplet shape changes the farther the drop moves from the nozzle, which changes the effects of the drop on the substrate. Accordingly, variations in the distance from the print head to the substrate can cause irregular effects on the printed image.
In addition to problems in jetting ink onto contoured surfaces, the curing of UV inks that requires sharply focused UV energy to deliver sufficient curing energy to the ink is difficult to achieve where the surface is contoured.
For the reasons stated above, ink jet printing has not been successful on contoured materials and other three-dimensional substrates, particularly printing with UV curable inks in ink jet printing processes.
An objective of the present invention is to provide for the printing onto three-dimensional substrates, particularly onto highly textured fabrics, tufted or irregular fabrics and other materials, contoured surfaces such as quilts, and mattress covers, and onto molded, stamped and otherwise shaped rigid or semi-rigid materials, and other three-dimensional surfaces. A particular objective of the invention is to print onto such surfaces with ink jet or digital printing processes. One more particular objective of the invention is to print onto such substrates with UV curable inks.
According to the principles of the present invention, printed images are applied to three-dimensional substrates with printing elements that are moveable relative to the plane of the substrate being printed. In certain embodiments, the invention provides a wide-substrate ink jet printing apparatus with print heads that move toward and away from the plane of a substrate to maintain a fixed distance between the nozzles of the printhead and the surface onto which the ink is being jetted. The variable distance over the plane of the substrate allows a controlled and uniform distance across which the ink is jetted.
In one preferred embodiment of the invention, the printing element is an ink jet print head set having a plurality of heads, typically four, each for dispensing one of a set of colors onto the substrate to form a multi-colored image. To maintain the constant distance or to otherwise control the distance, one or more sensors is provided to measure the distance from the print head or from the print head carriage track to the point on the substrate on which ink is to be projected. The sensors generate reference signals that are fed to a controller that controls a servo motor on the print head carriage. The print head is moveably mounted to the carriage, for example on a ball screw mechanism, and is moveable toward and away from the plane of the substrate by operation of the servo motor.
In a preferred embodiment of the invention, each print head of a set of four different color print heads is separately moveable relative to a common print head carriage, and is connected to one of a set of four servo motors by which its position relative to the plane of the substrate is capable of control relative to the positions of the other print heads. The print heads of the set are preferably arranged side by side in the transverse direction on the carriage so that one head follows the other across the width of the substrate as the carriage scans transversely across the substrate. Each head has a plurality of ink jet nozzles thereon for dispensing a given color of ink in a corresponding plurality of dots, for example 128 in number, that extend in a line transverse to the carriage, which is in a longitudinal direction perpendicular to the scan direction of the carriage. Two laser or optical sensors are provided on the carriage, one on each side of the heads, so that a distance measurement of the surface to the substrate can be taken ahead of the print heads when the heads are scanning in either direction. The controller records the contour of the substrate ahead of the print heads and varies the position of each print head, toward and away from the substrate plane, as each print head passes over the points at which the measurements were taken, so that each of the independently moveable heads follows the contour and maintains a fixed distance from the surface being printed.
While it is preferred to adjust the position of the print head or nozzle thereof relative to the substrate which is fixed on a printing machine frame, the substrate surface can alternatively be positioned relative to a print head that is maintained at a fixed vertical position on the frame.
Preferably, UV ink is printed onto material and the cure of the ink is initiated by exposure to UV light. UV curing lights may be mounted on the print head carriage, one on each side of the print head set, to expose the printed surface behind the heads. With or following the exposure to the UV light, the printed textile substrates or other textured or porous fabric is subjected to heat, preferably by blowing heated air onto the material downstream of the printing station, which extends the UV light initiated curing process and removes uncured components of the ink. With quilted bedding fabric materials, UV curable ink is jetted onto the fabric and the jetted ink is exposed to UV curing light to cure the ink preferably to about 90 to 97% polymerization, with the fabric bearing the partially cured, jetted ink then heated in a hot air blower curing oven at which the UV light initiated polymerization continues, uncured monomers are vaporized, or both, in order to produce a printed image of UV ink that contains a low quantity of uncured monomer or other ink components, for example, less than 0.01%.
Where UV ink is jetted onto a highly textured fabric such as a mattress cover ticking material, the ink is jetted at a dot density of from about 180xc3x97254 dots per inch per color to about 300xc3x97300 dots per inch per color. For certain common UV inks, four colors of a CMYK color palette are applied, each in drops or dots of, for example, about 75 picoliters, or approximately 80 nanograms, per drop, utilizing a UV ink jet print head. A UV curing light head is provided, which moves either with the print head or independent of the print head and exposes the deposited drops of UV ink with a beam of about 300 watts per linear inch, applying about 1 joule per square centimeter, thereby producing at least a 90% UV cure. The fabric on which the jetted ink has been thereby partially UV cured is then passed through an oven where it is heated to about 300xc2x0 F. for from about 30 seconds up to about three minutes. Forced hot air is preferably used to apply the heat in the oven, but other heating methods such as infrared or other radiant heaters may be used. Similar parameters may be used for cloth covered rigid panels such as office partitions.
When printing onto contoured material, the distance from the print heads to the substrate where the ink is to be deposited can be determined by measuring the distance from a sensor to the substrate ahead of the print heads and mapping the location of the surface. For bidirectional print heads that move transversely across the longitudinally advancing fabric, providing two distance measuring sensors, one on each of the opposite sides of the print heads, are provided to measure the distance to the contoured fabric surface when the print heads are moving in either direction. For some inks and for sufficiently rigid materials, a mechanical rolling sensor may be used, for example, by providing a pair of rollers, with one roller ahead of, and one head behind, the print head so that the average distance between the two rollers and a reference point on the print head can be used to control the distance of the print head from the plane of the substrate. To achieve this, one or more print heads can be mounted to a carriage having the rollers on the ends thereof so that the mechanical link between the rollers moves the print head relative to the plane of the substrate. In most cases, a non-contact sensor, such as a laser or photo eye sensor, is preferred in lieu of each roller. The outputs of two sensors on opposite sides of the print heads can be communicated to a processor, to measure the distance from the heads to the fabric ahead of the bidirectional heads, to drive a servo motor connected to the print head to raise and lower the head relative to the substrate plane so that the print heads move parallel to the contoured surface and jet ink onto the fabric across a fixed distance.
These and other objects of the present invention will be more readily apparent from the following detailed description of the preferred embodiments of the invention.